L-735,524 (of Merck & Co.) and 3TC (of Glaxo, Inc.) are investigational drugs which are currently being tested in adults who are infected with human immunodeficiency virus type-1 (HIV-1), the virus that causes the acquired immuno-deficiency syndrome (AIDS). The objective of this study is to evaluate the antiviral activity of the combination of L-735,524, ZDV, and 3TC in patients previously treated with ZDV alone and to assess the development of viral resistance to all three agents over 52 weeks of therapy.